Pair of photo-emission electron micrographs showing how heat-treatment of steel changes the austenite phase to martensite. Steel is made by the addition of carbon to iron. Above red heat, steel is in a face-centred cubic phase, known as austenite (left). Very rapid cooling produces a brittle transformation product, martensite. This austenite was held at 1070 degrees C & then cooled to 850 C in 8 seconds, to produce platelets of martensite (right). The photo-emission electron microscope forms its image from the light emitted when the specimen is bombarded with electrons. Magnification: x280 at 35mm size. Microcosmos, fig. 7.8, page 130.